Topological Insulators: a New Playground for Spintronics

Controlled spin-resolved transport is the holy grail of spintronics. A major breakthrough in condensed matter physics – the discovery of topological phases of matter (Nobel Prize in Physics 2016) – has opened perspectives to realize robust, spin-polarized transport on the surface of peculiar semiconductors, so called topological insulators (TIs). This phenomenon is intimately connected to the symmetries of matter, and it was soon established that exotic transport pathways may also be realized, for instance, via crystal lattice symmetries (topological crystalline insulators, TCI) and even in bulk (Weyl semimetals). Versatility of topological phases, which are not limited to any particular class of compounds with certain “chemical” markings, inspires the quest for new representatives.

In pursuit of topological insulators, we have focused on bismuth-rich halides with layered and chain-like structures [1], and have identified three families of candidate materials. The present talk will highlight representatives of each group – Bi14Rh3I9 (3D weak TI) [2–4, 8], Bi2TeI (3D weak TI and TCI) [5,6] and Bi3TeI (“topological metal”) [6], and Bi4I4 (3D strong TI) [7] – studied in intense cooperation with RWTH Aachen (Germany); DIPC San-Sebastian (Spain); EPFL and Berkeley National Laboratory (USA) over the past five years. Meticulous synthesis and crystal-growth optimizations were complemented by thorough crystal structure elucidation and characterization of structural defects. Predictions of topological properties from first-principles calculations were consequently verified by ARPES, STM/AFM experiments in case of Bi14Rh3I9 [8] and Bi4I4 [7]. Very recent high-pressure experiments on Bi4I4 unravel unexpected new avenues [9].

Bio:
Anna Isaeva has received her MSc and PhD in Materials Science and Inorganic Chemistry at Lomonosov Moscow State University, Russia (1999–2008, group of Prof. Boris A. Popovkin). Her thesis comprised synthesis optimization, crystal growth, structure characterization and band-structure calculations of complex metal chalcogenides. During the PhD phase, she stayed at Technische Universität Dresden, Germany, for 6 months as a holder of the INTAS Young-Scientist-Fellowship. In 2009–2010 she conducted her postdoctoral research project at EMAT center (Electron microscopy for materials science), the University of Antwerp (group of Prof. Gustaaf Van Tendeloo) where she acquired expertise in modern TEM methods. Since mid 2010 she has been working as a research assistant at Technische Universität Dresden, first as a co-worker for DFG-funded projects with a focus on band-structure calculations and real-space characterization of chemical bonding, and later on as a principal investigator of projects dedicated to correlated and itinerant magnetism and topological insulators. She is currently leading the research topic on topological insulators in the group of Prof. Michael Ruck and is finalizing her habilitation about the chemical aspects of these materials.